Surface foaming can be a problem in storage and treatment tanks where large volumes of liquid/slurry are stored and stirred, mixed, or agitated. For example, in activated sludge secondary treatment plants, slurries in the tank are stirred, mixed, or agitated in order to suspend solids in the liquid prior to emptying the tank. Similarly, surface foaming can be a problem in anaerobic digesters. The foam may take the form of bubbles and/or scum on the surface of the liquid/slurry in the tank. If the foaming problem is not addressed, the foam uses up volume in the tank, or the tank can overflow.